1. Field of the Invention
The present invention relates generally to electrical protection devices, and particularly to electrical protection devices with safety features.
2. Technical Background
Ground fault circuit interrupters (GFCIs), and arc fault circuit interrupters (AFCIs) are examples of protective devices in electric circuits. These devices may be disposed in a receptacle that is subsequently installed in a wall box. The receptacle has line terminals for connection to the power line, and load terminals for connection to a load. The load terminals include receptacle contacts and feed-thru terminals. The receptacle contacts are configured to accommodate the blades of a plug connector, which are inserted to provide power to a load. Feed-thru terminals, on the other hand, are configured to accommodate wires which are connected to one or more additional receptacles, known as a downstream receptacles. The downstream receptacle may include a string of downstream receptacles that comprise a branch circuit of an electrical distribution system. Each of the aforementioned protective devices have interrupting contacts for breaking the connection between the line terminals and load terminals when the protective device detects a fault condition. The connection is broken to interrupt the load current and thereby remove the fault condition. Fault conditions include those that result in risk electrocution of personnel, or fire.
There are several safety issues that heretofore have not been addressed in an integrated way. The first type of problem are fault conditions such as ground faults and arc faults that may result in electrocution or fire, respectively. The second type of problem involves the inadvertent insertion of objects, such as paper clips and screwdriver blades into the receptacle contact openings. This situation also involves an electric shock hazard. A third type of problem relates to the introduction of contaminants into the device during shipping, handling, or storage, or following installation. Contaminants such as water, corrosive compounds, particulate matter, insects, and etc. may enter the device via the receptacle contact openings. Any of these contaminants may result in the failure of the protective device.
With respect to the first problem, historical problems with these devices include the possibility of the line wires being connected to the load terminals during installation, also known as miswiring. A variety of methods have been used to prevent, or attempt to prevent, mis-wiring, with varying levels of success. Labels and installation instruction sheets have been used to prevent mis-wiring, but can be ignored by the installer. Historical problems include a defective solenoid driving device. Solenoid burn-out has been revealed by testing the protective with a test button, but the result of the test can be ignored by the user.
In one approach that has been considered, the receptacle contacts and feed-thru terminals may remain electrically connected irrespective of whether the interrupting contacts are open or closed. Should the power line be improperly connected to the feed-thru terminals, e.g., mis-wired, the receptacle contacts remain energized even if one of the predetermined fault conditions is present in the load that is connected to the receptacle contacts via the plug connector. One drawback to this approach is that a mis-wire condition results in the receptacle contacts being accessible while the fault condition persists.
In another approach that has been considered, the lack of protection to the receptacle terminals when the protective device is mis-wired has only been partially addressed. This approach employs a circuit that prevents interrupting contacts from remaining closed when the protective device has been mis-wired. Since the interrupting contacts do not remain closed, there is lack of power to the down-stream receptacles which are connected to the line terminals. Typically, the open or closed condition of the interrupting contacts are visually indicated to the user by the position of a button, indicator lamp, or audible alarm. When the visual indicator signals that the interrupting contacts are in an open condition, or there is loss of power on the downstream receptacles, the installer is thereby prompted to correct the mis-wired condition. This approach also has its drawbacks. If the branch circuit does not include downstream receptacles, in which case the feed-thru terminals are not used, the installer is not alerted to the mis-wire condition by denial of power to either the downstream branch circuit or to the receptacle contacts. Lack of protection of the receptacle contacts is only evident to the installer if the signal or absence of signal from the visual indicator is understood. Visual indication is much more easily ignored than power denial and the mis-wire condition may not be corrected.
There have been proposed solutions for the second problem. In one approach that has been considered, an electrical receptacle includes shuttered openings to prevent the insertion of foreign objects into the receptacle contact openings. The shutter is disposed within the receptacle housing. The shutter is configured to open only when the blades of an electrical plug are inserted into the openings. One drawback to this approach, is that the shutter is a stand-alone mechanism that is not integrated with any mis-wire protection feature. Another drawback is that this approach does not take into account the third problem, e.g., the shutter does not prevent the introduction of water, corrosive compounds, particulate matter, insects, and other contaminants into the device via the receptacle contact openings. Another drawback is that the shutter is not disposed within the receptacle housing and is subject to being easily removed by the user.
What is needed is means for detecting a mis-wire condition that may be employed in conjunction with a physical barrier that prevents insertion of a plug into the receptacle until such time as power has been properly connected to the line terminals of the protection device. What is further needed is a physical barrier that is effective in preventing the second type of hazard from occurring after the device has been properly wired. Finally, the physical barrier must prevent the introduction of water, corrosive compounds, particulate matter, insects, and other contaminants into the device via the receptacle contact openings.